Metallic blasting and abrasive material



Patented Dec. 7, 1943 METALLIC BLASTING AND ABRASIVE MATERIAL John T.Eash, Westfield, and Kenneth A. De

Longe, Cranford, N. 1., assignors to The International Nickel Company,Inc., New York, N. Y., a corporation of Delaware No Drawing. ApplicationDecember 29, 1942, Serial No; 470,518

7 Claims. (o1. 51-309) The present invention relates to metallicblasting and abrasive material used in processes where the blastingmaterial is thrown at high velocities against an object by. air or othergas pressure or by mechanical force to clean or cut the object or toobtain an abrading effect, and more particularly to cast iron materialwhich is to be crushed and used as grit in such processes.

It has been proposed to make grit and the like, i. e., cast iron shot orother particles which are crushed or fractured and are angular or havesharp corners or edges, of hard white cast iron or of soft malleablizedcast iron, but such blasting and abrasive material was not completelysatisfactory. Unalloyed white iron grit possessed high hardness, butlacked the desired toughness and shattered on impact. Some modifiedcompositions exhibited moderate improvement in toughness, but grithaving such composition still suffered from the disadvantage ofshatterin upon impact with the material being blasted and of havingrelatively short service life- Malleablized cast iron grit, having amicrostructure containing principally ferrite and temper carbon,possessed higher toughness than white iron grit, but its hardness andwear resistance was at a much lower level. Although many attempts weremade to remedy these and other shortcomings none, as far as we areaware, was entirely successful when carried into practice commercially.

We have discovered that an improved combination of properties, includinghigh hardness, can be obtained by using a special composition formetallic blasting and abrasive material intended primarily to be used asgrit, and the like, i. e., in

a form having angular or sharp corners or edges.

It is an object of the present invention to provide grit having animproved combination of properties.

It is another object of the invention to provide a metallic blasting andabrasive material having improved toughness at high hardness levels.

It is a further object of the invention to provide ametallic blastingand abrasive material having increased service life.

It is still another object of the invention to provide an improvedmartensitic-austenitic-carbidic alloy cast iron grit which has animproved combination of toughness, decreased tendency to shatter andhigh hardness.

It is also an object of the invention to provide an improved cast irongrit having a simple composition and improved impact resistance at'.highhardness levels.

Generally speaking, the present invention provides an alloyed cast irongrit and the like to be used in a form having angular or sharp cornersor edges and made of cast iron containing about 2% to 4% carbon, up toabout 0.8% manganese, about 2% to 3% silicon, about 0.25% to 3.5%nickel, and about 0.07% to 1.1% chromium, the nickel and chromium beingpresent in a ratio of about 2:1 to 4: 1, e. g., a nickel to chromiumratio of about 3:1 or more. While manganese is not essential, whensulfur is present about 0.2% to 0.8% manganese should also be present.The grit provided by the present invention may also contain smallamounts of incidental or minor constituents and impurities added forknown purposes or present as the result of commercial practice, e. g.,sulfur, phosphorus, titanium, molybdenum, etc. Thus, the cast iron gritmay contain about 0.02% to 0.2% of sulfur, about 0.03% to 1% ofphosphorus, about 0.01% to 0.05% of titanium, etc. It'is to beunderstood that when the term balance substantially iron is used herein,it is desired to exclude incidental or minor constituents or impuritieswhich may be present in such amounts as occur in commercial products orin amounts not adversely affecting the desired properties of the castiron grit.

In carrying the invention into practice, it is preferred to maintain thecomposition within the ranges of about 2.7% to 3.5% carbon, about 0.3%to 0.6% manganese, about 2% to 2.5% silicon, about 0.75% to 1.5% nickel,about 0.25% to 0.5% chromium, andthe balance substantially iron. A

satisfactory composition contains about 2.9% to 3.1% carbon, about 2.4%to 2.5% silicon, about 0.4% to 0.6% manganese, about 0.75% to 1.25%nickel and about 0.25% to 0.4% chromium.

It is a critical feature of the improved grit that a. balancedcomposition be maintained within the ranges set forth hereinbefore. Ifthe silicon content falls below the amounts set forth, the high hardnessof the grit provided by the invention is no longer obtained. It has beenfound that the effect of silicon in cast iron grit is not the same as inordinary cast iron castings. High silicon contents in grit apparentlypromote high hardness and brittleness and favor the formation ofmartensite, whereas, in ordinary castings, high silicon contents promotelow hardness and low toughness and favor the formation of graphite andpearlite. Nickel and chromium in the amounts set forth hereinbefore areessential to obtain the desired improved toughness, combined with highhardness, to give good service life.

The improved cast iron grit provided by the invention contains a largeproportion of martens-- ite and has a microstructure constitutedsubstantially entirely or carbide, i. e., cementite, in a matrix ofmartensite and austenite. It is essential that the grit contain a smallamount of austenite, but the amount should not exceed about 15% of thetotal matrix of martensite and austenite, e. g., about5% to 10% of thematrix should be austenite and the balance martensite. When the term"martensite is used, it is intended to include not only themicro-constituent commonly referred to as martensite, but is alsointended to include smaller amounts of other austenitic decompositionproducts, such as bainite, and troostite. In the grit provided by theinvention, the carbide is markedly refined and the matrix is partiallyaustenitic as compared to the more massive carbides and the entirelymartensitic matrix of similar plain malloyed cast iron grit.

In order that those skilled in the art may have a better understandingof the present invention, the properties of grit compositions made inaccordance with the invention are compared with unalloyed cast iron inthe table set forth hereinafter. Compositions No. 1 to No. 4 in thetable also contained about 3.5% carbon, about 0.5% manganese, about0.08% sulfur, and about 0.6% phosphorus. Compositions No. 5 to No. 8contained about 3.17% carbon, while No. 9 to No. 12 contained about2.93% carbon and No. 13 to No. 16 contained about 2.85% carbon. Allcontained about the same amounts of manganese, sulfur and phosphorus asNo. 1 to No. 4.

No. 1 to No. 4 were cast by pouring into cold water held at 55 to 60 F.,whereas No. 5 to No. 12 were cast. in hot water held at 105 to 110 F.and No. 13 to No. 16 were cast in quenching oil held at 70 to 75 F. Itwill benoted that for the alloyed grit compositions provided by theinvention, and illustrated by No. 2 to No. 4, No. 6 to No. 8, No. to No.12, and No. 14 to No. 16, the maximum hardness as indicated by theVickers hardness number (V. H. N.)-is obtained at the lower alloycontents and the maximum toughness, as indicated by the impact values,is obtained at the higher alloy contents. The impact values set forth inthe table indicate the minimum blow in inch-pounds which was required tocause fracture of the shot and were obtained in the following manner.- Adrop test procedure was used consisting of dropping a weight of about ofthe weight of the hammer in pounds and the minimum height of the fall ininches required to fracture the shot was taken as the impact strength.

The grit compositions provided by the invention have the desired highhardness with improved toughness. For example, No. 10 and No. 11 whichare suitable for grit have a high-hardnessof over 900 V. H. N. combinedwith improved toughness compared to unalloyed specimen No. 9 which wasnot made in accordance with the invention. In some cases the hardness aswell as the toughness are improved. Thus, No. 10, No.

0.6 pound upon a single shot, starting from a height of about two inchesand increasing the height of fall successively by one inch incrementsuntil fracture of the shot occurred. The product ness than similarunalloyed compositions. It will be noted that the silicon content ofthese compositions is at a higher level than in No. 2 to No. 4, and No.6 to No. 8 and that the quenching medium was such as would produce aslower cooling rate than that used for No. 2 to No. 4. Changes in thecooling rate or the sacrifice of some hardness for the sake of increasedtoughness may. require some'adjustment in the alloy content to obtainthe desired combination of properties. In

general, too rapid cooling rates tend to reduce the hardness and shouldbe avoided. Thus, casting a composition containing about 1.56% nickel,0.52% chromium, 2.96% carbon, 2.46% silicon, 0.50% manganese, 0.08%sulfur and 0.01% phosphorus, which is very similar to No. 12, in coldwater at 42 F. produced too rapid cooling and resulted in a soft producthaving a high impact value of 7.3 but a hardness of only 567 V. H. N.which is unsatisfactory for grit. In general, the cooling rate should besuch as to produce a hardness of at least about 750 V. H. N.

The present invention is applicable to the production of metallicblasting and abrasive material, particularly to the production ofmaterial which is to be crushed or fractured and used in that form, e.g., as grit. A brief description of some blast cleaning processes,apparatus and illustrations of the diflerences in surfaces cleaned bygrit and by shot may be foimd in Metals Handbook, 1939 ed., pages 1142and 1143. The use of grit blasting for purposes other than cleaning arealso well known to those skilled in the art, e. g., for cutting,abrading surfaces to be enameled, etc.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and of the appendedclaims.

We claim:

1. Cast iron grit containing about 2% to 2.5% silicon, about 0.75% to1.5% nickel, about 0.25% to 0.5% chromium, the nickel and chromium beingpresent in the ratio of about 3:1 to 4:1.

2. Cast iron grit containing about 2% to 2.5% silicon, about 0.75% to1.5% nickel, about 0.25% to 0.5% chromium, the nickel and chromium beingpresent in the ratio or about 3:1, said material being characterized bya microstructure comprised of carbide, martensite and a small amount ofaustenite.

3. As an article of manufacture, a cast iron particle having angular orsharp edges and of size suitable for grit blasting and the like made ofcast iron comprising about 2% to 4% carbon, about 0.2% to 0.8%manganese, about 2% to 3% silicon. about 0.25% to 3.5% nickel, and about0.07% to 1.1% chromium, the nickel and chromium being present in theratio of about 2:1 to 4:1, said particle being characterized by amicrostructure comprised substantially entirely of carbide, martensiteand a small amount of austenite.

4. As an article of manufacture, a cast iron particle of size and shapesuitable for grit blasting made or cast iron comprising about 2% to 4%carbon, about 0.2% to 0.8% manganese, about 2% to 3% silicon, about0.25% to 3.5% nickel, about 0.07% to 1.1% chromium, the nickel andchromium being present in the ratio 0! about 3: 1, and the balancesubstantially all iron.

5. Cast iron grit made of cast iron particles containing about 2.7% to3.5% carbon, about 0.3% to 0.6% manganese, about 2% to 2.5% silicon,about 0.75% to 1.5% nickel, about 0.25% to 0.5% chromium, the nickel andchromium being present in the ratio of about 3:1 to 4:1, said grit 2obeing characterized by a microstructure comprised of carbide, martensiteand a small amount of austenite.

6. Cast iron grit made of cast iron particles containing about 2% to 3%silicon, about 0.25%

to 3.5% nickel, about 0.07% to 1.1% chromium,

the nickel and chromium being present in the ratio of about 2:1 to 4:1,said grit being charactenzed by a microstructure comprised of carbide,martensite and a small amount of austenite.

7. Cast iron grit made of particles of cast iron containing about 2% to3% silicon, about 0.25% to 3.5% nickel, about 0.07% to 1.1% chromium,the nickel and chromium being present in the ratio of at least about 3:1and up to about 4:1, said grit being characterized by a Vickers hardnessnumber of at least about 750.

JOHN T. EASH. KENNETH A. DE IDNGE.

